The present invention relates to arrangements for separating and cleaning gaseous and liquid substances with cyclones and especially treating liquid suspensions that are used in the production of paper and board.
For purifying suspensions of the paper and pulp industry of coarser and/or finer impurities and dirt particles, mainly centrifugal cleaning apparatuses, i.e. hydrocyclones are used, or later, shorter, cyclones when reference is made to an individual cyclone.
The through flow of fiber suspension is enormous in a conventional paper or pulp mill and correspondingly a large amount of cyclones are needed. A centrifugal cleaning arrangement may comprise even hundreds of cyclones that are combined to form centrifugal cleaner groups. Cyclone groups may be connected in successive series or they can operate parallel connected. Individual cyclones may get clogged or otherwise require periodical cleaning or other maintenance. In that case the cyclone has to be detached from the group or to be dismantled.
Cyclones of a centrifugal cleaning plant are prone to clogging, especially at the reject end, and an individual cyclone has to be removable, dismountable or replaceable. Further, cyclones may wear in operation and require periodic replacement. In prior art centrifugal cleaner groups, convenient detaching and connecting of cyclones has been solved in many various ways. U.S. Pat. No. 4,572,787 discloses how a mutual connection of the feed and accept channels of the centrifugal cleaner group and the cyclones is effected with a push-in coupling, which is very easy to detach and connect. Additionally, the cyclones are mutually replaceable. However, the inlet, outlet and reject channels remain open while the cyclone is detached. Thereby the operation of the whole group of cyclones is to be stopped and the contents of the apparatus may leak out even abundantly. Further, the substance contained in the cyclone group may be pressurized, hot or otherwise detrimental and even dangerous for a person doing the maintenance work.
Within processes, detaching of an individual cyclone and thereby stopping of the whole group is not always even possible without disturbing other earlier or later production stages or without causing remarkable reduction in the production capacity. In the starting phase the operation of a cyclone is normal only after the cyclone has reached its full velocity, so that stopping of a whole group also causes a substantial quality problem when all the cyclones are to be restarted.
Closing valves may be mounted between the cyclone and the centrifugal cleaner group, such as in publication U.S. Pat. No. 3,989,628, whereby the maintenance operations for an individual cyclone may usually be performed without causing essential disturbance for the process.
However, these individual closing valves consume space, which hardly is adequate around tightly accommodated cyclones. Further, the operation and the actuators of the closing valves require space in order to allow access to the closing valve and ensure its operation. Especially, when horizontally located double cyclones are used, lack of space often prevents closing of the valves, specifically with respect to the inlet and outlet channels. The use of closing valves in groups of centrifugal cleaners for closing the cyclone is not very common, because of costs of valves needed and their mountings.
Closing of a reject channel is usually possible to accomplish more easily, since there is considerably more space at the narrower reject end. A pressurized reject system is additionally often provided with a regulation valve used for regulating the reject ratio, which regulation valve can in most cases be used also as a closing valve. In a free reject system, the reject conduit is not pressurized so that depending on its structure it may even be possible to leave it unclosed without any significant leakage or disturbance for the process.
Usually the closing valves are to be used in a certain order for not mixing various fractions produced by the process. Usually simultaneous closing of the feed and accept flows is advantageous. At least the inlet connection having the highest pressure should be closed first and the outlet connection immediately thereafter to avoid overpressure. Separate valves that are positioned in different directions, such as e.g. in publication U.S. Pat. No. 3,989,628, involve great risks of operating in wrong order or other malfunction, and some of the closing valves may be left open by mistake and thus cause a disturbance in the process. An individual separate closure may also easily be left unopened after replacement or re-mounting of a cyclone, whereby the cyclone will not function or functions defectively. When the number of cyclones is huge, the probability of human errors is emphasized.